Large aperture wide angle lens

ABSTRACT

A bright 10-element-in-8-group super-wide angle lens has a back focus of at least 1.6f, and includes ten consecutively designated successive lenses, the first lens being a convex lens, the second and third lenses being concave meniscus lenses, the fourth lens being a concave meniscus lens cemented to the fifth convex lens to form a doublet, the sixth lens being a convex lens, the seventh lens being a concave lens cemented to the eighth convex lens to form a negative doublet, the ninth lens being a convex meniscus lens and the tenth lens being a convex lens. The focal length of the lens system, as well as the focal length, radius of curvature, index of refraction and Abbe number of certain of the lens elements are selected to fall within designated maximum and minimum parameters to provide low aberration and optimum brightness.

United Sta Takahashi et a1.

Dec. 9, 1975 LARGE APERTURE WIDE ANGLE LENS Inventors: Yasuo Takahashi; Ryota Ogawa, both of Tokyo, Japan Asahi Kogaku Kogyo Kabushiki Kaisha, Tokyo, Japan Filed: June 28, 1974 Appl. No.: 484,205

Assignee:

US. Cl. 350/214; 350/176; 350/196 Int. Cl. G02B 11/34 Field of Search 350/214, 196

References Cited UNITED STATES PATENTS Mori 350/214 X Primary Examiner-John K. Corbin Attorney, Agent, or FirmWolder & Gross 57 ABSTRACT A bright lO-element-in-S-group super-wide angle lens has a back focus of at least 1.6f, and includes ten consecutively designated successive lenses, the first lens being a convex lens, the second and third lenses being concave meniscus lenses, the fourth lens being a concave meniscus lens cemented to the fifth convex lens to form a doublet, the sixth lens being a convex lens, the seventh lens being a concave lens cemented to the eighth convex lens to form a negative doublet, the ninth lens being a convex meniscus lens and the tenth lens being a convex lens. The focal length of the lens system, as well as the focal length, radius of curvature, index of refraction and Abbe number of certain of the lens elements are selected to fall within designated maximum and minimum parameters to provide low aberration and optimum brightness.

2 Claims, 10 Drawing Figures U.S. Patent Dec. 9, 1975 Sheet 1 of 2 3,924,935

FIG. I

M75 D/SMET/OA/ meaM/mz/wmmmv FIG. 2A FIG. 28 FIG. 26 FIG. 20

US. Patent Dec. 9, 1975 Sheet 2 of2 3,924,935

FIG. 3

FIG. 40

FIG. 4A

LARGE APERTURE WIDE ANGLE LENS BACKGROUND OF THE INVENTION The present invention relates to improvements in lenses, and in particular to an improved wide angle lens system of the retrofocus type.

In recent years, remarkable developments have been made in wide angle lenses and great progress has been realized, particularly in the manufacture of retrofocus type super-wide angle bright lenses. Nevertheless because of the wide-angle characteristics of such lens systems, the systems are usually subject to high distortion and high aberration, and lack the desired brightness.

SUMMARY OF THE INVENTION In accordance with the invention there is provided a bright lO-element-in-8-group super-wide angle lens with minimum aberration, having a back focus of I.6f or greater, and satisfying each of the following condi 50 v8+v9+vl0l3 70 Additional objects and advantages of the invention will become apparent in the course of the following specification when taken in connection with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic elevational view of a wide angle lens system embodying the present invention, in, one embodiment thereof; I

FIGS. 2(A 2(B), 2(C) and 2(D) are a series ofcomparative graphs illustrating the curves of the lens system of FIG. 1 with respect to various types of aberration;

FIG. 3 is a schematic elevational view similar to FIG. 1, but showing a modified embodiment of wide angle lens system in accordance with the present invention; and

FIGS. 4(A), 4(B), 4(C) and 4D are a series of comparative graphs illustrating the various aberration curves obtained by the lens system of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION Referring in detail to the drawings, and in particular to FIG. 1, there is shown a wide angle lens system constituting a preferred embodiment of the invention. The reference numerals I, 2, 3, 4, 5, 6, 7, 8, 9, and consecutively designate the first to the tenth lenses respectively from the rear lens 1 to the front lens 10.

The first lens I is a convex lens having a surface S1 which faces toward the subject to be photographed, and an opposed surface S2. The surface 81 has a greater radius r than the radius of curvature r of the surface S1. The lens 1 has a thickness d, and an index of refraction designated n hereinafter. from the The second lens 2 and the third lens 3 are both concave meniscus lenses. Lens 2 has a surface S3 which faces the image and has a radius of curvature r greater than the radius of curvature r, of the opposite surface S4. The lens 2 has a thickness d;, and a refractive index designated n The surface S3 is spaced a distance d from the surface S2 of lens 1. Lens 3 has a surface S5 which faces the image and has a radius of curvature r greater than the radius of curvature r of the opposite surface S6. The lens 3 has a thickness 41,, and its surface S5 is spaced a distance d, fromthe surface S4 of lens 2. inwardly of the second and third lenses is arranged a filter 20 which, in this embodiment, is not included in the number of lenses.

The fourth lens 4 is a concave meniscus lens having a surface S7 of smaller radius of curvature r than the opposite face thereof, the latter face being cemented to the confronting face of the fifth lens 5 to define a single surface S8 of the doublet unit subsystem so formed. The surface 58 has a radius of curvature r The fourth lens 4 has an index of refraction n and a thickness d and its surface S7 is spaced a distance d, from the surface S6 oflens 3. The fifth lens 5 is a convex lens having a non-cemented surface S9 of radius of curvature r a thickness d and an index of refraction n The sixth lens 6 is a convex lens with opposed surfaces S10 and S11, a thickness d and an index of refraction m The surface S10 is spaced by a distance (1,, from the surface S9 of lens 5, a diaphragm being interposed in this spacing between lenses 5 and 6. The seventh concave lens 7 and the eighth convex lens 8 are cemented together at their complementary faces, defining a surface S13 to form a negative doublet lens component. The seventh lens 7 has an outer surface S12, a thickness d and a refractive index n The surface S12 is spaced a distance d from surface S11 of lens 6. The eighth lens 8 has an outer surface S14. a thickness d and a refractive index n,;.

The ninth lens 9 is a convex meniscus lens having a surface S15 facing toward the image and being of a large radius of curvature r than the radius of curvature r of its opposite surface S16. The lens 9 has a thickness d a refractive index n and its surface S15 is spaced a distance d from the surface S14 of lens 8.

The tenth lens 10 is a convex lens having opposed surfaces S17 and S18, a thickness d and a refractive index n The surface S 17 is spaced a distance d from the surface S16 of lens 9. The Abbe numbers of the lenses 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 are respectively designated V V V V V V V V V and V FIG. 3 illustrates a modified embodiment of wide angle lens system constituting ten lenses of similar construction and arrangement as the lenses of the previous embodiment, and again designated respectively as lenses 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. The previous description of the embodiment of FIG. 1 applies equally to the embodiment of FIG. 3, except that the filter 20 is eliminated. The specific quantitative details of the lens elements of FIG. 3 differ from those of the embodiment of FIG. I as will be presently set forth in detail.

The wide angle lens systems illustrated in both FIG. 1 and FIG. 3 are made to satisfy the following conditions (1) through (5) inclusive:

3 wherein:

F is the combined focal length of entire system, F,, is the composite focal length of lenses 1 to i, 11,- is the refractive index in d-line of the ith lens, 1 is the Abbe number of ith lens, d, is the spacing or lens thickness between the jth surface and the +1 )th surface, and 1-,. is the radius of curvature of the kth lens. The functions and applications of the conditions 1) comatic aberration excessively. Conversely, when r lr exceeds 1.5, an inner comatic aberration will readily be developed with a light ray having a comparatively small incident angle. It is difficult to correct such an inner comatic aberration at the other lens surfaces.

Condition (4):

This is a condition for correcting the comatic aberration. When 11-, exceeds 0.4 and is larger than n it becomes difficult to balance the outer coma developed at to (5), designated above, to be satisfied by the lens systhe lens surface $14 in the range from comparatively tems of the present invention are described in detail as small to larger incident angles. This naturally is associfollows: ated with r and 41, Conversely, when n, exceeds 11 by Condition l a value smaller than 0.1, the chromatic aberration can- It is evident that in a wide angle retrofocus lens, the not be corrected and it becomes meaningless for the front lens group has a negative focal length. When F, 15 lenses to be cemented together. 1s a negative value shorter than F/0.95, the lens can Condition (5): cover a wide angle but cannot have a sufficient bright- This is a condition for controlling and correcting the ness due to aberrations developed at various lens surchromatic aberration developed at various lenses infaces. in particular, such an arrangement gives rise to cluding the seventh one. When an inferior comatic aberration. When the front lens group has a focal length longer than F/0.6, the aberra- 10 tions are decreased to some extent. However, to obtain 3 a back focus longer than the intended value, the rear lellls group CQHStrUCFed & s z. is smaller than 50, the chromatic aberration can be corg ere mcrTasmg egree 2 rected only imperfectly. To eliminate this advantage W1 ang e cannot e covere out the seventh lens must bear an excessive burden. Howg l Size ever, this will have an adverse influence over the char- 9 g b d d d bl acteristics of the seventh lens to a large extent, because l L Q s e 9 eslrla y this lens has an influence of great importance over the Y 3;? roma 2. S "L e balance in aberration as is defined by conditions (3) n a men to con 1t1on t e proper oca engt and on the other hand when range of the front lens group must be sat1sfied. When the focal length F, is negative and shorter than 8 9 w F/0.25, the sixth positive lens must compensate for this. Accordingly the sixth lens will provide an increased aberration, losing the balance. On the contrary, when F is positive and shorter than F/0.25, the lens surexceeds t thelmended e e t Cannot be atta ned befaces 57 to 59 have to bear an increased burden, cause var1ous disadvantages w1ll appear 1n var1ous abthereby developing aberrations and adversely i m errat1ons due to a small refractwe 1ndex of the lens maing the back focus. As a result, an increased burden will 40 tehal' be applied to the-rear lens group, The invention w1ll be more fully understood w1th ref- Condition (3 )2 erence to the following Table l which sets forth, by way This condition represents a relationship between r 0f Illustration, 8 speeltlc e p of the lehs system and r which has a delicate influence over the aberrah the first embothmeht Thls table tion balance. This condition is essential for maintainglves Selected Values of the of eufvatures "1 ing, especially, the balance in spherical aberration. h g '"18 of each of the lens surfaces 51 t9 the When r is either equal to r or has a larger absolute dlstahees 1 to 17 between each f e and the next value, the spherical aberration will increase excessively SucCeSSh/e Surface, the d'hhe rehact'Ve hdex to in the positive direction so that it can hardly be covered of each of the lenses, and the Abbe P p 1 t0 10 of by any other lens Surfaces, For example, trying to each of the lenses. The lens system 1n this example has pensate the spherical aberration at the lens surface S14 a focus F 112-4, the focal length la-s of the first is essentially impractical, because this will increase the three lenses 15 given the focal length F of the first five lenses 1s g1ven as l589.825.

' TABLE I F 1:2.4 Angle ofview Zw= 95.20 r 326.282 d =40.61 n 1.64000 1 60.2 r 949.626 d z 0.49 r 207.067 1,,= 9.98 n 1.79590 v 44.2 r 88.29l d 38.62 r,,=230.832 d,= 5.99 n ,=1.5s913 u;,=6l.l r 80.421 d 5089 Filter thickness 7.30 r 1 276.609 d 11.59 n 1.75700 v,= 47.9 r 60.873 0 78.01 11 ,=1.74950 v,,= 35.2 r ,=-349.170 d 20.119 r 740.533 d..,= 19.45 n 1.65160 11,: 58.6 r =-100.524 11., 10.47 r,,= 81.327 d,, 4.97 n -=1.s051s v,= 25.4 r,,,= 228.884 d. 7.50 n L48749 v..=70.1 r,,- 340.745, d,,= 9.88 r., 409.070 1,,= 21.91 n ,=1.51633 vt= 641 r..,=104.702 d,, 0.49

TABLE I-continued In addition, the following Table 11 sets forth Seidels v with an increased angle of view. In this instance, the coefficients for each of the lens surfaces S1 to S18 of focal length of the first three lenses is given as the lens system illustrated 1n FIG. 1: 10 120.642, and the focal length of the first five lenses is TABLE 11 Number of lens surface 1 11 111 P V Filter 510 0.015 0.029 0.057 0.053 0215 s11 17.527 1.434 0.117 0.392 0.042 s12 21535 0.924 0.040 0.548' 0.025 513 0680 0.367 0199 0.052 0.135 s14 1600 -1.033 O.667' 0.096 0.493 815 0.110 0.179 0.291 0.083 v 0.337 516 1.732 0.099 0.006 0.325 0.019 $17 0059 0.087 0.128 0.073 0.297 s18 8.200 0.579 0.041 0.269 0.022

The following Table 111 sets forth, by way of illustragiven as 1515.152.

TABLE 111 F 100 1:2.4 Angle of view 2u= 96.80 r 316.035 d 40.70 n 1.64100 11,: 56.9 r 860.727 d 0.50 r 192.992 d 10.00 11 1.78800 :1 47.5 r 85.423 d 38.70 r 224.740 d 6.00 n 1.58913 11; 61.1 r 79.827 d 54.40 r 73.245 :1 11.60 n 1.75500 v,,= 52.5 r 76.470 0 78.15 n 1.74950 :1 35.2 r ,=358.257 d 16.05 r,..= 742.100 1..,= 45.35 n 1.65160 v 58.6 1,, 99.663 6,,= 10.00 r, 81.765 d,,= 6.00 n =1.80518 v 25.4 r,.,= 243.745 d 6.00 n 1.48749 v,.= 70.1 r 307.472 d, 9.90 r.,=-409.540 d,,= 21.95 n 1.56873 v.,= 63.1 r...=1 12.317 d 0.50 r 5.77.870 d,,= 36.15 n,.,= 1.77250 8...: 49.6 r,,.= 160.725 F -120.642 F, ,4;H 5= 1515.152

tion, a specific example of lens system shown in the sec- The following Table IV sets forth the Seldels coeffiond embodiment of FIG. 3. The values given are of the cients for each of the lens surfaces 81 to S18 of the lens same type as in Table l, and in this example the lens system illustrated in FIG. 3. system is shown as having a focus of F 100, 12.4, but

7 8 TABLE lV-contmued Number of lens surface 1 ll 11 P V 513 0.556 0.317 -O.l80 0.049 0.l30 S14 1.682 l.070 0.680 0.107 0.500 S15 0.112 0.186 0.306 0.089 0.359 S16 1.314 0.125 0.012 0.323 0.032 517 0.060 0.089 0.131 0.075 0.304 S18 8.001 0.520 0.034 0.271 0.020 SUM 1.011 0.204 0.024 0.095 0.271

The highly superior optical characteristics and performance of the lens system of FIG. 1, having the values designated in Table I, are shown in the group of aberration curves illustrated in FIGS. 2(A), 2(B), 2(C) and 2(D). Similarly the optical characteristicsof the lens system of FIG. 3, having the values designated in Table III, are shown in the group of aberration curves illustrated in FIGS. 4(A), 4(B), 4(C) and 4(D).

While preferred embodiments of the invention have been shown and described herein, it is obvious that numerous changes, omissions and additions may be made in such embodiments without departing from the spirit and scope of the invention.

What is claimed is:

1. A wide angle lens system including ten lenses consecutively successively designated from the front to the rear, the lens surfaces being consecutively successively designated, with cemented faces defining a single sur-' face and a filter interposed between the third lens and the fourth lens, said lens system possessing the following dimensions and values:

r 326.282 d 40.61 n 1.64000 11, 60.2 r z 949.626 d 0.49

r 207.067 d 9.98 11 1.78950 v 44.2 r 88.291 d 38.62

Filter thickness 7.30

r 276.609 d 11.59 11 1.75700 11, 47.9 1' 60.873 d 78.01 n 1.74950 v 35.2 r 349.l70 d 20.89

1' 740.533 d,,,: 39.45 n 1.65160 v 58.6 r =100.524 d 10.47

r,-, 598.995 d 36.08 n 1.77250 v 49.6 r -l62.162

wherein rj is the radius of curvature of the jth lens surface, dj is the axial distance between the jth lens surface and the (j 1)th surface, n,- is the refractive index of the ith lens and vi is the Abbe number of the ith lens,

the fourth and fifth lenses being cemented at their mating confronting faces to form a first doublet and the seventh and eighth lenses being cemented at their mating confronting faces to form a second doublet.

20 2. A wide angle lens system including ten lenses consecutively successively designated from the front to the 1 rear, the lens surfaces being consecutively successively designated with cemented faces defining a single surface said lens system possessing the following dimensions and values:

wherein rj is the radius of curvature of the jth lens surface, dj is the axial distance between the jth lens surface and the (j 1) lens surface, n,- is the refractive index of the ith lens and vi is the Abbe number of the ith lens,

the fourth and fifth lenses being cemented at their mating confronting faces to form a first doublet and the seventh and eighth lenses being cemented-at their mating confronting faces to form a second doublet. 

1. A wide angle lens system including ten lenses consecutively successively designated from the front to the rear, the lens surfaces being consecutively successively designated, with cemented faces defining a single surface and a filter interposed between the third lens and the fourth lens, said lens system possessing the following dimensions and values:
 2. A wide angle lens systeM including ten lenses consecutively successively designated from the front to the rear, the lens surfaces being consecutively successively designated with cemented faces defining a single surface said lens system possessing the following dimensions and values: 